## Reading Astronomy News: The Mystery of Titan’s Expanding Orbit

##### 08/07/2020

By **Stacy Palen**

Titan’s orbit is growing, which is unexpected! This article might be appropriate when discussing orbits, outer planet moons, or resonances.

Below are some questions to ask your students based on this article.

**1) What did astronomers EXPECT to find out about Titan’s orbit, before undertaking this study?**

*Answer: They expected to see that Titan’s orbit was unchanging.*

**2) How much does Titan’s orbit grow each year? Give an example of a common, everyday object that is about that size.**

*Answer: 11 centimeters (cm). This is a little bit shorter than a pen or pencil, so each year, Titan’s orbit grows by less than a pencil length.*

**3) Compare this rate to the rate at which the orbit of Earth’s Moon grows. Is Titan moving away from Saturn faster or slower than the Moon moves away from Earth?**

*Answer: The Moon moves away at 4 cm per year. Titan moves away from Saturn almost three times faster.*

**4) For how many years did the Cassini spacecraft orbit Saturn?**

*Answer: Cassini orbited from 2004 to 2017, so approximately 13 years.*

**5) During that time, how much did Titan’s orbit expand in total?**

*Answer: 11 cm times 13 years is 143 cm, just shy of 1.5 meters.*

**6) The semi-major axis of Titan’s orbit is 1,221,870,000 meters. By about what fraction did this value grow during Cassini’s visit to Saturn?**

*Answer: 1.43 m / 1.22187 X 109 m is about 1 in a billion. Dang.*

**7) What is “resonance-locking tidal theory?” How does this account for the loss of energy from Titan’s orbit, due to the orbit growing larger?**

*Answer: This is the idea that if the moon tidally flexes Saturn, in resonance with Saturn’s internal ringing, energy can be transferred from the moon’s orbit to Saturn’s internal motion.*

What other questions would you ask your students based on this article? Feel free to leave suggestions in the comments!